The present invention relates to a solid mass for mercury recovery, characterised by its method of preparation. This solid mercury recovery mass contains a solid mineral dispersant or support, copper and sulphur combined at least partially in the form of copper sulphide.
The present invention likewise has as an object a method of preparing a precursor of a solid mercury recovery mass and also the precursor obtained by the said method.
The solid masses of the present invention may be variously termed: absorption, recovery, extraction or trapping masses.
U.S. Pat. No. 4,094,777 describes a method of producing a mercury recovery mass comprising the incorporation of a copper compound into a mineral support followed by sulphuration at a temperature below 300.degree. C.
Sulphuration according to the method described in this patent is carried out by means of a gaseous agent, for example hydrogen sulphide, or a solution of a mineral sulphide in water or in an organic solvent, for example an aqueous solution of sodium sulphide, potassium sulphide or ammonium sulphide.
The masses obtained exhibit high activity and are relatively inexpensive. However, the preparation of these recovery masses does have a number of substantial drawbacks.
Thus, when sulphuration is carried out by means of gaseous hydrogen sulphide (H.sub.2 S), obtaining a recovery mass having sufficient activity normally requires working at elevated temperatures, for example around 200.degree. C., which is a penalty in energy and equipment cost. Furthermore, H.sub.2 S is a toxic and malodorous gas.
The use of sulphide solution, for example an aqueous solution of ammonium sulphide, makes it possible to work at a relatively low temperature for example between 0.degree. and 100.degree. C. However, ammonium sulphide is a toxic compound which is also readily decomposable, thereby complicating its use.
The use of other sulphides (of sodium . . . ) brings additional cations into the mass, which is undesirable.
According to patent application EP-A-107582, a mercury recovery mass is prepared by impregnation of a carrier by means of an organic solution of elementary sulphur or an aqueous solution of a sulphur compound which is decomposable into elementary sulphur at a temperature below 150.degree. C.
After drying and volatilisation of the organic compound or after the aforesaid decomposition, a carrier or support is obtained with a dispersion of non-molten sulphur in the free state.
U.S. Pat. No. 4,474,896 describes a mercury recovery mass obtained by bringing into contact a carrier impregnated with a metallic cation capable of forming an insoluble polysulphide, with a mixture of polysulphide and sulphide.
In the tests described, CaCl.sub.2 supports treated by elementary sulphur have been prepared. The results obtained in the processing of fluids containing a mercury charge are poor: the effluent displays excessive quantities of mercury.